We intend to continue our studies on the chromosomal localization of human genes using somatic cell hybridization techniques. Interspecies hybridization between mouse and human cells will be the major focus of this research. In addition, we intend to study the regulation of mouse and human nucleolus organizer activity and 28S ribosomal RNA synthesis in mouse-human somatic cell hybrids segregating either mouse or human chromosomes. We also plan to select for drug resistant mutants of mouse and human teratocarcinoma cells, to produce mutant mice using the drug resistant mouse teratocarcinoma cells, to produce mouse-human teratocarcinoma cell hybrids able to induce teratocarcinomas in nude mice and to produce mice carrying specific human genes.